yul-phaser: A few more tweaks to ensure that signedness conversions do not cause warnings

- Don't cast booleans to int when the result gets assigned to an unsigned type. Relace them with ifs.
- Use unsigned initializer for a variable declared in a lambda capture.
- Unsigned abs() of a difference of unsigned values.

test/yulPhaser/Population.cpp

@@ -135,7 +135,7 @@ BOOST_FIXTURE_TEST_CASE(makeRandom_should_get_chromosome_lengths_from_specified_
 	size_t maxLength = 5;
 	assert(chromosomeCount % maxLength == 0);
 
-	auto nextLength = [counter = 0, maxLength]() mutable { return counter++ % maxLength; };
+	auto nextLength = [counter = 0ul, maxLength]() mutable { return counter++ % maxLength; };
 	auto population = Population::makeRandom(m_fitnessMetric, chromosomeCount, nextLength);
 
 	// We can't rely on the order since the population sorts its chromosomes immediately but